Phase change materials that are used in memory devices may exhibit at least two different states and therefore may be used to store a bit of data. These states may be referred to as the amorphous and crystalline states. These states may be distinguished since the amorphous state generally exhibits higher resistivity than the crystalline state. Generally, the amorphous state involves a more disordered atomic structure.
Phase change materials in a memory cell may be programmed by altering a resistance of the material. However, variations in the materials, fabrication processes, and operating environment may cause the resistance of a phase change material to vary or drift after the phase change material is programmed. Thus, some cells originally programmed to one state may undesirably change to a different state after programming or the resistance of some cells may drift to a level that may not provide for adequate sense margins between the states.